Posted by
Kenneth Sloan-2 on
Nov 07, 2019; 8:34pm
URL: http://imagej.273.s1.nabble.com/Calculate-the-concentration-in-a-CT-image-tp5022621p5022622.html
Knowing nothing about this particular application, I will assume nothing.
So far, you seem to have two pairs of (CT Number, concentration):
(loCT, loConcentration)
(hiCT, hiConcentration)
You want to convert intermediate (or more extreme?) CT numbers into concentrations.
Method a) assume everything is linear, and just use linear interpolation:
u = (CT-loCT) / (hiCT-loCT)
CT = loConcentration + (u * (hiConcentration-loConcentration))
I DO NOT RECOMMEND this method!
Method b) gather more data - measure CT numbers for known concentrations, fit a function to your measurements,
and evaluate this function at new measured CT numbers.
I might start by measuring the CT number for (loConcentration + hiConcentration)/2. If (by some miracle)
this turns out to be = (loCT + hiCT) / 2, then go to Method a) Otherwise, measure at ¼ and ¾. Continue
sub-dividing until you are happy with a low-degree polynomial that fits your data.
The usual caveats about fitting a predictor to data apply - in particular, it is dangerous to EXTRAPOLATE from
the measured values. Interpolation is much safer. And, avoid high-degree polynomials which may overfit your data.
Also consider exponential/log functions. If you know anything about the physics of the imaging, use that.
--
Kenneth Sloan
[hidden email]
Vision is the art of seeing what is invisible to others.
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>
> I am processing a CT image. They have two different brines mixed together. One fluid is high CT number. Its concentration is 2mol/L (KI doped). Another brine is pure water and its CT number is low.
>
> I want to relate the CT number to the concentration value. (Let's assume that the brightest part is 2 mol/L fluid and pure water is lowest CT number)
>
> Can anybody help me with the above question?
>
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